Dentifrice formulations comprising peroxide are known and useful for cleaning and whitening teeth. The peroxide can bleach the teeth, remove stains, and kill cariogenic bacteria. However, peroxide compounds are highly reactive, and consequently difficult to formulate. Moreover, hydrogen peroxide can spontaneously decompose to form oxygen gas (O2) and water, so that on storage, the dentifrice containers may bloat, burst or leak, and the remaining formulation will not have enough peroxide remaining to clean and whiten teeth effectively. Some initially comprise very high levels of peroxide, which decomposes over time, so that the exact amount of peroxide delivered on application is variable and largely depends on how long and under what conditions the dentifrice has been stored.
Abrasives comprising calcium phosphate salts, such as calcium pyrophosphate, dicalcium orthophosphate dihydrate, tricalcium phosphate, and calcium polymetaphosphate are useful in dentifrice materials, as in addition to providing an abrasive action which cleans the teeth, such salts provide a source of calcium and phosphate which can help build and repair the teeth. Calcium salts such as calcium carbonate are also commonly used as abrasives. However, under oxidizing conditions, calcium ions can readily form calcium peroxide (CaO2) and calcium oxide (CaO, also known as quicklime), which is highly reactive and corrosive, reacting exothermically with water for example to form calcium hydroxide (Ca(OH)2). Thus dentifrices using calcium salts are not preferred for formulation with peroxide.
Abrasive-free dentifrices comprising peroxide also present formulation challenges. While the problem with interaction with the abrasive is removed, the peroxide may still react with other components of the formulation and/or decompose to release O2.
By exposure to aqueous environments, as in the oral cavity, the PVP-H2O2 dissociates into individual species (PVP polymer and H2O2). The PVP-H2O2 complex is generally comprised of about 80% by weight polyvinyl pyrrolidone and 20% by weight H2O2. Single phase whitening dentifrice compounds comprising PVP-H2O2 complexes are described, e.g., in WO/2007/037961, and its parent US Pub. No. US 2007-0071695 A1, the contents of which are incorporated herein by reference.
While there are numerous publications of gels comprising peroxide, such gels are generally for use with dental trays or strips, rather than for application using a toothbrush, and such gels are not necessarily suitable for use as a dentifrice because they may adhere to the toothbrush, rather than rinsing off easily, and leave the consumer with an unpleasant experience due to the lack of foaming provided by the product.
There is thus a need for improved peroxide dentifrice formulations that are stable for long-term storage and are suitable for everyday consumer use.